The present disclosure relates to three-dimensional imaging, and more specifically, to the reconstruction of three dimensional surfaces using structured lighting.
As the processing speed and memory capacity of computers have continued to increase, along with advances in computer graphics software, the interest in imaging both the geometry and surface texture of three-dimensional (xe2x80x9c3Dxe2x80x9d) objects has also increased. Numerous applications of such technology which for many years were anticipated have begun to be realized. The use of 3D representations has expanded in many areas, including entertainment, animation, industrial design, engineering, achieving, commercial advertising, catalogs, and xe2x80x9cvirtual realityxe2x80x9d visits to actual places (e.g., cities and museums).
Various techniques have in turn developed to capture this information. Some are mechanical, some are purely based on images. Each system proposes different tradeoffs. The main parameters to be considered include: cost, accuracy, ease of use, and speed of acquisition. So far most commercial 3D scanners have favored accuracy over other parameters. However, while accurate, these systems tend to be very expensive.
One example of a mechanical system uses physical contact with the object to measure its surface. A robot arm xe2x80x9cfeelsxe2x80x9d the object and records the variations in dimension. The object may be rotated or otherwise adjusted to allow for multiple measurements. This type of system is typically expensive, bulky and slow.
Another group of systems uses active lighting, such as a laser or LCD projector. Typically these systems also use motorized transport of the object. The object is lit by projected light and rotated to provide views from multiple angles. While such systems are very accurate, they are also typically very expensive and bulky. Another disadvantage of lasers is that they are potentially dangerous to the operator""s eyes, reducing the applicability of these systems to consumer use.
Some computer vision researchers have considered taking a different approach, favoring cost and ease of use while sacrificing some accuracy and speed. A number of ways of obtaining information on 3D shapes from more passively acquired images have long been known: stereoscopic disparity, texture, motion parallax, (de)focus, shading and specularities, occluding contours and other surface discontinuities. Unfortunately, the single passive cue that gives reasonable accuracy, stereoscopic disparity, has two major drawbacks: (a) it requires two cameras, and (b) it is typically ineffective on untextured surfaces. Accordingly, such a system is not inexpensive because of multiple cameras. In addition, because the great majority of industrially manufactured objects do not have textured surfaces, stereoscopic disparity is not suitable for a large number of applications.
The inventors have determined that a better technique for representation is found using shadow rather than lasers or multiple cameras. Accordingly they have developed the methods and apparatus for capturing 3D surfaces based on structured lighting described in the present disclosure.
The present disclosure describes methods and apparatus providing techniques for capturing the surface of three-dimensional (xe2x80x9c3Dxe2x80x9d) objects using structured lighting. The movement of shadow across the 3D objects is optically recorded. Variation in brightness on the surface provides a cue for triangulation. By analyzing the variation in brightness of a particular point on the surface, the location of that point is determined based on the movement of the shadow. With known locations for a camera and a light source, the coordinates in space of the point is triangulated. By repeating this process, a collection of coordinates is created. Those coordinates are then used to reconstruct the 3D surface.
In accordance with one embodiment of the invention a pencil or other object with a straight edge is moved between a light source and a scene of 3D objects. The pencil casts a shadow across a surface of the scene. A camera located below the moving pencil records the scene and shadow. The deformation of the edge of the shadow caused by the contours of the 3D objects is triangulated with calibration information to determine coordinates in space of points on the surface. Those coordinates are then used to reconstruct the 3D surface.
A second embodiment uses a projection of a grayscale pattern upon a scene. A camera records the scene during the projection. The projection is a sinusoidal pattern of brightness. A sequence of frames is projected, each offset from the last, such that the sinusoidal pattern appears to translate across the scene. Thus each point on the scene receives the entire spectrum of brightness contained in the sine wave of the pattern. Using variation in brightness, coordinates of each point in space are determined by triangulation and so the 3D surface is reconstructed.